Ercag Pince

Synthesis of graphene on gold

Here we report chemical vapor deposition of graphene on gold surface at ambient pressure. We studied effects of the growth temperature, pressure, and cooling process on the growngraphene layers. The Raman spectroscopy of the samples reveals the essential properties of the graphenegrown on gold surface. In order to characterize the electrical properties of the growngraphene layers, we have transferred them on insulating substrates and fabricated field effect transistors. Owing to distinctive properties of gold, the ability to growgraphene layers on gold surface could open new applications of graphene in electrochemistry and spectroscopy.

Investigation of high frequency performance limit of graphene field effect transistors

Extremely high field effect mobility together with the high surface coverage makes graphene a promising material for high frequency electronics application. We investigate the intrinsic high frequency performance limit of graphene field effect transistors limited by the charge impurity scattering. The output and transfer characteristics of graphene field effect transistors together with the high frequency performance are characterized as a function of impurity concentration and dielectric constant of the gate insulator. Our results reveal that graphene transistors could provide power gain at radio frequency band.

Disorder-mediated crowd control in an active matter system

Living active matter systems such as bacterial colonies, schools of fish and human crowds, display a wealth of emerging collective and dynamic behaviours as a result of far-from-equilibrium interactions. The dynamics of these systems are better understood and controlled considering their interaction with the environment, which for realistic systems is often highly heterogeneous and disordered. Here, we demonstrate that the presence of spatial disorder can alter the long-term dynamics in a colloidal active matter system, making it switch between gathering and dispersal of individuals. At equilibrium, colloidal particles always gather at the bottom of any attractive potential; however, under non-equilibrium driving forces in a bacterial bath, the colloids disperse if disorder is added to the potential. The depth of the local roughness in the environment regulates the transition between gathering and dispersal of individuals in the active matter system, thus inspiring novel routes for controlling emerging behaviours far from equilibrium.

Graphene mode-locked multipass-cavity femtosecond Cr 4+ : forsterite laser

We report, for the first time to our knowledge, the use of graphene as a saturable absorber in an energy-scaled femtosecond Cr4+: forsterite laser. By incorporating a multipass cavity, the repetition rate of the original short resonator was reduced to 4.51xa0MHz, which resulted in the generation of 100xa0fs, nearly transform-limited pulses at 1252xa0nm with a peak power of 53xa0kW. To the best of our knowledge, this is the highest peak power obtained from a room-temperature, femtosecond Cr4+: forsterite laser mode locked with a graphene saturable absorber. The corresponding pulse energy was 5.3xa0nJ with only 24xa0mW of average output power. The saturation fluence and modulation depth of the GSA were measured to be 25u2009u2009μJ/cm2 and 0.74%, respectively. The nonlinear effects in the Cr4+: forsterite medium that limit further power scaling were also investigated by using different output couplers.

Non-Boltzmann stationary distributions and non-equilibrium relations in active baths

NON-BOLTZMANN STATIONARY DISTRIBUTIONS AND NON-EQUILIBRIUM RELATIONS IN ACTIVE BATHS Aykut Argun M.S. in Physics Advisor: Giovanni Volpe September 2016 Most natural and engineered processes, such as biomolecular reactions, protein folding, and population dynamics, occur far from equilibrium and, therefore, cannot be treated within the framework of classical equilibrium thermodynamics. Here, we experimentally study how some fundamental thermodynamic quantities and relations are affected by the presence of the non-equilibrium fluctuations associated with an active bath. We show, in particular, that, as the confinement of the particle increases, the stationary probability distribution of a Brownian particle confined within a harmonic potential becomes non-Boltzmann, featuring a transition from a Gaussian distribution to a heavy-tailed distribution. Because of this, non-equilibrium relations (e.g. Jarzynski equality, Crooks fluctuation theorem) cannot be applied. We show that these relations can be restored by using the effective potential associated with the stationary probability distribution. We corroborate our experimental findings with theoretical arguments.

Study of microparticles' anomalous diffusion in active bath using speckle light fields (Presentation Recording)

Particles undergoing a stochastic motion within a disordered medium is a ubiquitous physical and biological phenomenon. Examples can be given from organelles as molecular machines of cells performing physical tasks in a populated cytoplasm to human mobility in patchy environment at larger scales. Our recent results showed that it is possible to use the disordered landscape generated by speckle light fields to perform advanced manipulation tasks at the microscale. Here, we use speckle light fields to study the anomalous diffusion of micron size silica particles (5 μm) in the presence of active microswimmers. The microswimmers we used in the experiments are motile bacteria, Escherichia coli (E.coli). They constitute an active background constantly agitating passive silica particles within complex optical potentials. The speckle fields are generated by mode mixing inside a multimode optical fiber where a small amount of incident laser power (maximum power = 12 μW/μm2) is needed to obtain an effective random landscape pattern for the purpose of optical manipulation. We experimentally show how complex potentials contribute to the anomalous diffusion of silica particles undergoing collisions with swimming bacteria. We observed an enhanced diffusion of particles interacting with the active bath of E.coli inside speckle light fields: this effect can be tuned and controlled by varying the intensity and the statistical properties of the speckle pattern. Potentially, these results could be of interest for many technological applications, such as the manipulation of microparticles inside optically disordered media of biological interests.